And by reason hereof he ought (or, is bound, ὀφείλει), as for the people, so also for himself, to offer for sins. This obligation is evident in the ease of the high priests of the Law. Consequently, their sin offering for themselves, in the first place, was a prominent part of the ceremonial of the Day of Atonement, which the writer may be supposed to have especially in view (Leviticus 16:1-34).
But can we suppose any corresponding necessity in the case of Christ? The argument does not absolutely require that we should, since the obligation of the Levitical high priest may be adduced only in proof of his own experience of ἀσθενεία.
Christ, though under no such obligation, might still fulfill the requisites of a high priest, expressed in the case of sinful high priests by the obligation to offer for themselves; and we may (as Ebrard says) leave it to the writer to show hew he does fulfill them.
Whether, however, there was in Christ's own experience anything corresponding to the high priest's offering for himself will be considered under Hebrews 5:7, Hebrews 5:8.